1. Field of the Invention
This invention relates to an improved semiconductor laser device which prevents catastrophic degradation of the facets by the optical output and provides a high optical output.
2. Description of the Prior Art
What determines the upper limit of the optical output of a semiconductor laser device is catastrophic degradation of facets. The degradation gradually proceeds even when the laser device is operated at a low output and essentially determines the service life of the device. To prevent the catastrophic degradation of facets, the facets have conventionally been coated with an insulating film, but the degradation is likely to proceed from the interface between the insulting film and the semiconductor surface.
Thus it is preferred that the surface be coated with a semiconductor film which continues in a crystal arrangement the semiconductor forming the laser device. A method of accomplishing this object has been conceived in which, referring to FIG. 1, gutters 12 and 12' are provided on a substrate 1 in the proximity of facets 8, 9 and an active layer 3 is suspended so that the laser light comes out of the device in the proximity of the facets and is reflected by a transparent portion 4. The drawing is a sectional view in the plane parallel to the propagating direction of the laser light. Semiconductor layers 2 and 4 form clad layers while a semiconductor layer 5 forms a cap layer. Reference numerals 6 and 7 represent electrodes. However, it has been found in this method that the reflected light does not always return to the original active region, increasing the optical losses.
A semiconductor device as shown in FIG. 1 is disclosed in Japanese Patent Publication No. 54-85688 (1979), for example.